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Ultrasound Physics > Ch 12: Two-Dimensional Imaging > Flashcards

Ch 12: Two-Dimensional Imaging Flashcards

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1
Q

The mechanical transducer contains a ___ active element.

A

circular, disc-shaped

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2
Q

The mechanical transducer contains an active element that is phsically ___.

A

moved.

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3
Q

How many active elements does a mechnical transducer have?

A

one

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4
Q

What shape image is created by a mechanical transducer?

A

fan or sector-shaped

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5
Q

How is the beam steered with a mechanical transducer?

A

with a motor; mechanical steering

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6
Q

T/F? Mechanical transducers have a fixed focal depth.

A

true

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7
Q

Name two methods of fixed focusing.

A

internal - curved active element

external - curved acoustic element

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8
Q

What happens if the crystal gets damaged in a mechanical transducer?

A

The entire image is lost.

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9
Q

An ___ contains multiple active elements.

A

array

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10
Q

An array contains…

A

multiple active elements.

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11
Q

A ___ is the combination of the active element, wire and system electronics.

A

channel

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12
Q

A channel is the combination of…

A

the active element, wire, and system electronics.

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13
Q

How are the active element channels arranged in a linear phased array?

A

in a straight line

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14
Q

How are the active element channels arranged in an annular phased array?

A

as circular rings with a common center

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15
Q

How are the active element channels arranged in a convex phased array?

A

in a a bowed or arched line

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16
Q

How many active elements does a linear phased array have?

A

100-300

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17
Q

What shape image is created by a linear phased array transducer?

A

fan or sector-shaped

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18
Q

How is the beam steered with a linear phased array transducer?

A

a process called phasing; electronic steering

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19
Q

T/F? Linear phased array transducers have a fixed focal depth.

A

FALSE: The phased array system has controls that allow the sonographer to modify the depth and amount of focusing of the sound beam.

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20
Q

T/F? Phased array always means adjustable or multi-focus.

A

true

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21
Q

Modern phased array systems can transmit ___ beams down the ___ scan line, each with a ___ focal depth.

A

multiple, same, different

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22
Q

What happens if the crystal gets damaged in a phased array transducer?

A

inconsistent or erratic beam steering and focusing

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23
Q

How many elements in a phased array probe are used to create a single sound pulse?

A

ALL of them.

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24
Q

In a phased array system, how does the pattern of electrical spikes from the u/s system steer the sound beam in different directions?

A

The angle of the electrical spikes determines the angle of the beam.

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25
Q

The time differences between the electrical spikes firing are called…

A

phase delays.

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26
Q

The sound beam in a phased array tranducer is steered if…

A

the spike line has a slope.

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27
Q

When the spike line in a phased array tranducer is a straight line…

A

an unfocused sound beam is created.

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28
Q

The electronics within the u/s system that create electrical spike patterns is called…

A

the beam former.

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29
Q

How does the pattern of electrical spikes from the beam former focus the sound beam during transmission?

A

It fires the outer crystals before the inner crystals to create a curved pattern.

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30
Q

When the spike line in a phased array transducer is a curved line…

A

a focused sound beam is created.

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31
Q

How does a phased array system create images with multiple transmit foci?

A

By sending multiple sound beams down each scan line.

32
Q

T/F? Focusing may during reception as well as transmission.

A

true

33
Q

With dynamic receive focusing, the reflected sound is focused…

A

at many depths.

34
Q

An annular phased array has ___ active elements.

A

multiple ring-shaped

35
Q

What kind of beam steering does an annular phased array transducer have?

A

mechanical

36
Q

What is the primary advantage of annular phased arrays?

A

multiple transmit focal zones

37
Q

What shape image is created by an annular phased array transducer?

A

fan or sector-shaped

38
Q

What happens if a crystal gets damaged in an annular phased array transducer?

A

A horizontal portion on the image is lost.

39
Q

How many crystals does a linear sequential array tranducer have?

A

120-250

40
Q

What shape crystals does a linear sequential array tranducer have?

A

rectangular strips about 1 wavelength in width

41
Q

How is the beam steered in a linear sequential array transducer?

A

A small group of crystals are fired simultaneously, sequentially with other groups..

42
Q

How is the beam focused is a linear sequential array tranducer?

A

electronically

43
Q

This is achieved dynamically by introducing electrical delays in the signals returning from the transducer.

A

receive focusing

44
Q

What shape image is created with a linear sequential array tranducer?

A

rectangular

45
Q

What happens if one of the elements gets damaged in a linear sequential array tranducer?

A

A vertical portion of the image is lost.

46
Q

Can linear sequential array transducers steer sound beams electronically?

A

Yep. It creates a parallelogram-shaped image.

47
Q

What else are convex array transducers called?

A

curved and curvilinear

48
Q

How many crystals does a convex array tranducer have?

A

120-250

49
Q

What shape crystals does a convex array transducer have?

A

rectangular strips arranged side by side about 1 wavelength wide

50
Q

How is the beam steered in a convex array transducer?

A

Usually the crystals are fired simultaneously in groups sequentially across the surface

51
Q

How is the beam focused in a convex array transducer?

A

electronically and with dyname receive focusing

52
Q

What shape image does a convex array transducer create?

A

blunted sector-shaped

53
Q

What happens in a convex array transducer if one of the crystals are damaged?

A

A vertical portion of the image is lost.

54
Q

This is a combination of linear sequential and linear phased array technologies.

A

vector or virtual arrays

55
Q

How many crystals are in a vector array transducer?

A

120-250

56
Q

What shape crystals are in a vector array transducer?

A

rectangular-shaped strips arranged side by side in a line

57
Q

How is the beam steered in a vector array transducer?

A

electronically

58
Q

How is the beam focused in a vector array transducer?

A

electronically

59
Q

What shape image does a vector array tranducer create?

A

trapezoidal

60
Q

This is above-to-below accuracy in imaging.

A

slice thickness or elevational resolution

61
Q

What shape of element creates the best elevational resolution?

A

disc-shaped crystals

62
Q

The elevational resolution is ___ to the lateral resolution with disc-shaped active elements.

A

identical

63
Q

Which transducer types have the best elevational resolution?

A

mechanical and annular phased array (which have disc-shaped crystals)

64
Q

What determines elevational resolution in phased array, linear array, and convex array transducers?

A

An acoustic lens is used to create a thinner slice.

65
Q

One limitation of linear arrays is…

A

the inability to dynamically create thin slices.

66
Q

What newer types of transducers have improved slice thickness resolution?

A

1.5-D array transducer, which has crystals lined side-by-side and up-and-down.

67
Q

How many crystals does a 1.5-D array have?

A

700, 100x7

68
Q

What kind of array makes 3-D images?

A

2-D

69
Q

This creates an image from three dimensional data acquired during the ultrasound exam.

A

rendering

70
Q

Single element tranducers create sound beams that are ___ shaped.

A

hourglass

71
Q

Off-axis sound beams that extend outside of the main beam in the far zone in single element transducers.

A

side lobes

72
Q

What do reflections arising from within the side lobes do?

A

Degrade lateral resolution

73
Q

These are the off-axis sound beam that extend outside of the main beam in the far zone in array transducers.

A

grating lobes

74
Q

This process reduces the strength of side and grating lobes.

A

apodization

75
Q

In this process a crystal is divided into a group of smaller crystals called subelements.

A

subdicing

76
Q

This technique can be used to make a sound beam narrow over a greater range of depths and optimize lateral resolution.

A

dynamic aperture

Ultrasound Physics (23 decks)

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